In general, permanent waving of human hair is achieved by chemically breaking the sulfur to sulfur or disulfide cystine bonds occurring naturally in human hair and then reforming the cystine bonds while the hair is wrapped or curled on rods. The sulfur to sulfur cystine bonds in human hair maintain the hair in a naturally straight or curly configuration. In order to permanently reshape the hair into a lasting, different configuration, a significant percentage of the sulfur to sulfur bonds must be broken and then reestablished after the hair is reconfigured in a desired position, such as wrapped around a suitable mandrel or roller. In general, the sulfur to sulfur cystine bonds are broken with a composition containing a reducing agent and after the hair is wound into a curl formation around a rod or roller, the sulfur to sulfur cystine bonds are relinked or reestablished while the hair is in the curl formation by contacting the hair in the new formation with an oxidizing agent, such as hydrogen peroxide or a water-soluble bromate.
It is well known in the art of hair permanent waving that conventional reducing agents used in permanent waves to alter hair configuration result in a characteristic unpleasant odor in the hair. The intensity and duration of this unpleasant odor is formula dependent, depending, in particular, on the reducing agent used in the waving process. Conventional waving agents that are widely used are Ammonium Thioglycolate, Glyceryl Monothioglycolate (GMT), Sodium or Ammonium Bisulfite, and Cysteamine. All of these reducing agents leave residual odor on the hair, after reaction with the hair, that lasts from a day to one or two weeks. Some of the factors that play a role in the amount of odor left in the hair include the concentration and type of reducing agent, and the pH of the waving lotion. Some of the reducing agents are inherently more odoriferous than others. For example, it is widely known that Cysteine Hydrochloride is less odoriferous than GMT and the odor of Sodium Bisulfite is different and sometimes less objectionable than the mercaptans (thioglycolates).
The thiol reducing agents, such as Ammonium Thioglycolate, Ammonium Dithioglycolate, Glyceryl Monothioglycolate, and the like, produce malodor due to the formation of disulphides as shown below EQU K--S--S--K+2R--SH.fwdarw.R--S--S--R+2K--SH
The reducing agent step of the permanent waving process forms cleaved disulfide (sulfide) hair sites, and other reaction products. The cleaved disulfide (cysteine) hair bonds having reactive sulfur sites are then oxidized, to reestablish the hair bonds in the new hair configuration. Oxidation of the hair sulfur bonds present after reducing agent contact results in reestablished disulfide hair bonds as well as other side reactions products that are odiferous. In accordance with one embodiment the present invention, a carbonyl-containing compound, e.g., aldehyde or ketone, is added to hair that has been reduced with a thiol reducing agent, after rinsing and before the oxidation step, to react a portion of the reduced hair with the carbonyl associated with the permanent waving process.
Post-perm odor has been cited by clients as one of the major drawbacks of permanent waving. Many attempts have been made by formulators to address this odor problem with only limited success. For example in a pending U.S. application, Ser. No. 07/919,972, filed Jul. 27, 1992, Kolc, Abbott, and Nandagiri, disclose a reducing agent composition including a combination of Ammonium Thioglycolate and Cysteine free base to reduce processing odor and post-perm odor while maintaining all other performance characteristics. In a Japanese patent application 3-271214 Segawa et al. disclose a post-penn treatment composition containing acids to reduce the odor of Cysteamine waved hair.
Major marketers of permanent wave products in the United States have attempted to minimize the odor problem by using fragrances in the reducing agent-containing wave lotion and/or in the oxidizing agent-containing neutralizing composition.
Although these approaches are being practiced in the art, they are all only partially effective in overcoming the problems of post-perm odor. While not being bound to any specific theory on the mechanism of action, it is theorized that one of the reasons why there is persistent post-perm odor is due to certain odoriferous residues formed by reaction of hair aldehydes with the reducing agent. It is theorized that these residues are left in the hair after the waving process as a result of being chemically bound to hair protein or as a result of the residues being trapped within the hair matrix. Malodor is given off from these residues when the hair is wetted. Over time, with repeated shampooing of the hair, these residues are released from the hair, leaving the hair pleasant smelling again.
Addressing this problem by simply fragrancing the hair, without chemical bonding of the fragrance to the hair, in an attempt to mask the unpleasant odor is not effective since the masking fragrance is not long-lasting and does not prevent or reduce the formation of the odoriferous reaction products. We have found that more effective ways of dealing with post perm odor are: (1) minimize or prevent the formation of these malodor residues; and/or (2) compete for the olfactory receptor sites within the nose, with compounds that chemically bind to the hair and are faster in reaching the receptor sites than the malodor residues; and/or (3) change the distribution of odiferous reaction products such that the perceived odor is less objectionable than the odor resulting from the distribution of naturally occurring reaction products that are otherwise formed with natural hair-containing reactants, such as hair aldehydes.